For example, an assembled battery mounted on a hybrid car or an electric car is configured by a plurality of unit cells connected in series. The assembled battery generates a high voltage such as 200 V at the both ends thereof and supplies electric power thus generated to a driving motor. In such the assembled battery, it is necessary to detect and monitor the voltage across each of the unit cells so as to prevent an over discharge state and an overcharge state.
As the aforesaid voltage detection device for detecting a voltage across each of the unit cells, the device shown in FIG. 4 has been proposed (see patent literatures 1 and 2). As shown in this figure, a voltage detection device 100 detects a voltage across each of a plurality of unit cells C11 to Cmn (m and n are arbitrary integers) that are connected in series and constitute an assembled battery BH. That is, the assembled battery BH includes n blocks CB1 to CBn.
The voltage detection device 100 includes a plurality of battery monitoring ICs 201 to 20n for detecting voltage across each of the unit cells C11 to Cmn and a main microcomputer 300 which outputs detection instructions to the battery monitoring ICs 201 to 20n and receives detection voltage from the battery monitoring ICs 201 to 20n. The battery monitoring ICs 201 to 20n are respectively provided in correspondence to the blocks CB1 to CBn that are obtained by dividing the unit cells C11 to Cmn into plural blocks, in order to reduce a withstanding voltage. Each of the battery monitoring ICs is fed from the corresponding one of the blocks CB1 to CBn and then operated. The main microcomputer 300 is fed from a low-voltage battery different from the assembled battery BH and then operated.
It is necessary to perform a communication, in an electrically insulated state, between the main microcomputer 300 fed from the aforesaid low-voltage battery and the battery monitoring ICs 201 to 20n fed from the high-voltage assembled battery BH. That is, the communication is required to be performed using an insulation interface (I/F). As the insulation interface schema, a daisy chain schema having a high scalability is used. According to the daisy chain schema, the communication can be performed using the single insulation interface (I/F) 400. Further, the daisy chain schema can easily cope with increase and decrease etc. of the battery monitoring ICs 201 to 20n. 
As shown in FIG. 4, according to the daisy chain schema, the battery monitoring ICs 201 to 20n are connected in cascade, and only the battery monitoring IC 20n of the highest voltage as one of the battery monitoring ICs 201 to 20n is connected to the main microcomputer 300 via the insulation I/F 400 so as to be capable of communication. According to the aforesaid configuration, the battery monitoring IC 20n directly communicates with the main microcomputer 300 via the insulation I/F 400. Each of the battery monitoring ICs 201 to 20(n-1) communicates with the main microcomputer 300 via the insulation I/F 400 and the corresponding one or ones of the battery monitoring ICs 201 to 20n on the high-voltage side than the each battery monitoring IC.